Prospects for B s 0 $$ {B}_{(s)}^0 $$ → π 0 π 0 and B s 0 $$ {B}_{(s)}^0 $$ → ηη modes and corresponding CP asymmetries at Tera-Z

Abstract

Abstract The physics potential of measuring B s 0 $$ {B}_{(s)}^0 $$ → π 0 π 0 and B s 0 $$ {B}_{(s)}^0 $$ → ηη decays via four-photon final states at Tera-Z phase of CEPC or FCC-ee is investigated in this paper. We propose an electromagnetic calorimeter (ECAL) with both high energy resolution and excellent separation power to efficiently reconstruct π 0 and η from hadronic final states with high photon multiplicity. The resulting B-meson mass resolution is approximately 30 MeV, allowing 3 σ separation between B 0 and B s 0 $$ {B}_s^0 $$ . With the assistance of the b-jet tagging, the relative sensitivities to B 0 → π 0 π 0, B s 0 $$ {B}_s^0 $$ → π 0 π 0, B 0 → ηη, and B s 0 $$ {B}_s^0 $$ → ηη signal strengths at Tera-Z are projected as 0.45%, 4.5%, 18%, and 0.95%, respectively. Their dependence on various detector performances is also discussed. In addition, B 0 → π 0 π 0 and its two isospin-related modes are paid special attention due to their roles in the determination of the CKM angle α (ϕ 2). The anticipated precisions of their branching-ratio and CP-asymmetry measurements at Tera-Z are evaluated. We show that the measurement of the time-integrated B 0 → π 0 π 0 CP asymmetry at Tera-Z is complementary to B-factory ones. The precision on α combining Z- and B-factory results reaches 0.4°, lower than the systematic uncertainties attached to isospin breaking.

Keywords

• Bottom Quarks
• CKM Parameters